Engine

ABSTRACT

An engine includes: a cylinder head; a cam housing fastened to the cylinder head; a camshaft rotatably supported by the cam housing and supplied with lubricating oil; and a head cover fastened to the cam housing, wherein the cam housing includes a side wall extending along the camshaft, and an inner side surface of the side wall includes a recessed region recessed downward in a gravity direction.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2018-083912, filed on Apr. 25, 2018, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an engine.

BACKGROUND

There is known an engine in which oil for lubrication is supplied to a sliding portion such as a camshaft (for example, see Japanese Unexamined Patent Application Publication No. 2012-167647).

In some cases, the engine includes a cylinder head, a cam housing fastened to the cylinder head, and a head cover covering an upper side of the cam housing. These members are fastened via a seal member, which suppresses oil leakage from the engine. Herein, a temperature of the cylinder head is comparatively high due to the combustion of the fuel. However, a temperature of the cam housing is lower than that of the cylinder head, since the cam housing is spaced away from a combustion chamber. This leads to a temperature difference between the cylinder head and the cam housing. In particular, when the engine switches from a low load state to a high load state in a short period of time, this temperature difference increases. This temperature difference might increase a thermal expansion difference between the cylinder head and the cam housing, which might cause oil leakage between the cylinder head and the cam housing.

SUMMARY

It is therefore an object of the present disclosure to provide an engine that suppresses oil leakage.

It is an object of the present disclosure to provide an engine including: a cylinder head; a cam housing fastened to the cylinder head; a camshaft rotatably supported by the cam housing and supplied with lubricating oil; and a head cover fastened to the earn housing, wherein the cam housing includes a side wall extending along the camshaft, and an inner side surface of the side wall includes a recessed region recessed downward in a gravity direction.

The lubricating oil supplied to the camshaft increases its temperature due to the combustion of the engine, and splashes the inner side surface of the sidewall of the cam housing in response to the rotation of the camshaft Since the inner side surface of the side wall includes the recessed region recessed downward in the gravity direction, the oil is retained in the recessed region. This transmits the heat of the oil to the earn housing, which promotes heat exchange between the oil and the cam housing. This increases the temperature of the cam housing, which suppresses an increase in a temperature difference between the cam housing and the cylinder head, and also suppresses an increase in a thermal expansion difference between the cam housing and the cylinder head. It is thus possible to suppress oil leakage between the cylinder head and the cam housing.

The cylinder head may include a first seal surface that sandwiches a first seal member in cooperation with the side wall, the side wall may include a second seal surface that sandwiches a second seal member in cooperation with the head cover, and the recessed region may be provided at a position closer to the first seal surface than the second seal surface.

The inner side surface of the side wall may include an upper region continuous from the recessed region to an upper side in the gravity direction, and the upper region may be located outside the cam housing with respect to a line connecting an inner edge of the first seal surface and an inner edge of the second seal surface when viewed in a cross section perpendicular to a direction in which the camshaft extends.

The inner side surface of the side wall may be smoothly continuous from the upper region to the recessed region when viewed in the cross section perpendicular to the direction in which the camshaft extends.

The recessed region may extend along the camshaft.

The side wall may include a rib partially projecting inside the cam housing.

The side wall may include: an intake side wall located on an intake side; and an exhaust side wall located on an exhaust side, and the rib may be provided on the exhaust side wall.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view of an engine;

FIG. 2A is a top view of a cam housing, and FIG. 2B is a top view of a cylinder head;

FIG. 3A is a front view of the cylinder head and the cam housing, and FIG. 3B is a rear view of a chain cover;

FIG. 4A is a cross-sectional view taken along line A-A of FIG. 2A, and FIG. 4B is an enlarged view of a recessed region;

FIG. 5 is a cross-sectional view taken along line B-B of FIG. 2A; and

FIG. 6A is a partial top view of a cam housing according to a variation, and FIG. 6B is a cross-sectional view taken along line C-C of FIG. 6A.

DETAILED DESCRIPTION

FIG. 1 is an explanatory view of an engine 1. FIG. 1 illustrates X, Y and Z directions orthogonal to one another. In FIG. 1, the Z direction is parallel to the gravity direction, and the Y direction is parallel to a direction in which a crankshaft 15, a camshaft 53 on an intake side, and a camshaft 54 on an exhaust side extend. The engine 1 includes a cylinder block 10, a cylinder head 20, a cam housing 30, and a head cover 40. The cylinder head 20 is fastened to an upper side of the cylinder block 10. The cam housing 30 is fastened to an upper side of the cylinder head 20. The head cover 40 is fastened to an upper side of the cam housing 30, and the upper side of the cam housing 30 is covered with the head cover 40.

A plurality of cylinders 12 are provided in the cylinder block 10, and the cylinders 12 are arranged in a depth direction of FIG. 1. A piston 11 is vertically movably housed in each cylinder 12. When the pistons 11 move upward and downward, the crankshaft 15 rotates. The cylinder 12, the piston 11, and the cylinder head 20 define a combustion chamber CH whose volume is increased or decreased by the vertical movement of the piston 11. An oil pan 16 for storing lubricating oil is fastened to a lower side of the cylinder block 10. The oil is supplied to each sliding portion in the engine 1 via oil paths formed in the engine 1 by an oil pump, and is then recovered to the oil pan 16.

As for the cylinder head 20, a right side wall 23 and a left side wall 24 respectively located on the right side and the left side in HQ 1 extend in the V direction in which the cylinders 12 are arranged in a line. An intake port 21 and an exhaust port 22 are opened on an outer side surface of the right side wall 23 and an outer side surface of the left side wall 24, respectively. An intake pipe 81 and an exhaust pipe 82 are fastened to the right side wall 23 and the left side wall 24 so as to communicate with the intake port 21 and the exhaust port 22, respectively. Accordingly, the intake pipe 81 and the exhaust pipe 82 communicate with the combustion chamber CH through the intake port 21 and the exhaust port 22, respectively. Additionally, the cylinder head 20 holds an intake valve and an exhaust valve for opening and closing the intake port 21 and the exhaust port 22 in response to the rotation of the intake-side camshaft 53 and the exhaust-side camshaft 54, respectively. The camshafts 53 and 54 are rotatably supported by the cam housing 30.

FIG. 2A is a top view of the cam housing 30. The cam housing 30 includes a right side wall 33, a left side wall 34, a rear side wall 35, and a plurality of support walls 37. The rear side wall 35 extends continuously to the right side wall 33 and the left side wall 34 in the X direction, and is located at an end of the cam housing 30 in the −Y direction. The plurality of support walls 37 are supported between the right side wall 33 and the left side wall 34 facing each other, and each extend in the X direction. The support wall 37 rotatably supports the camshafts 53 and 54 so as to be spaced at a predetermined interval in the X direction. Intake cams 53 c and exhaust cams 54 c for respectively driving intake valves and exhaust valves of each cylinder are formed in the camshafts 53 and 54.

A sprocket 55 on the intake side and a sprocket 56 on the exhaust side are connected to ends of the camshafts 53 and 54 in the +Y direction, respectively. A timing chain 65 for interlocking the crankshaft 15 and the sprockets 55 and 56 is wound around the sprockets 55 and 56. As a result, when the crankshaft 15 rotates, the sprockets 55 and 56 also rotate via the timing chain 65. A chain cover 60 for housing the timing chain 65 is fastened to ends of the cam housing 30 and the cylinder head 20 in the +Y direction. In addition, the illustration of the chain cover 60 is simplified.

The lubricating oil stored in the oil pan 16 is supplied to the camshafts 53 and 54 via a plurality of paths. For example, the oil is supplied among the camshafts 53 and 54 and journal bearings via oil paths formed within the camshafts 53 and 54. The journal bearings are provided in the support walls 37 and hold the camshafts 53 and 54 for rotation. Further, the oil is supplied from a cam shower to the intake cams 53 e and the exhaust cams 54 c.

Seal surfaces 33 s, 34 s, and 35 s are formed on upper sides of the right side wall 33, the left side wall 34, and the rear side wall 35, respectively. The seal faces 33 s, 34 s and 35 s are continuous to one another and are substantially parallel to the XY plane. FIG. 2A illustrates a seal member CL3 on the seal surfaces 33 s, 34 s and 35 s. The seal member CL3 is a gasket made of rubber having oil resistance, specifically acrylic rubber, but is not limited thereto, and may be a liquid gasket described later. On the seal surfaces 33 s, 34 s and 35 s, a plurality of bolt holes, designated with numerical reference, into which respective bolts for fastening the cam housing 30 to the head cover 40 are inserted are formed. The seal member CL3 is located outside the plurality of bolt holes.

The cam housing 30 and the head cover 40 are fastened to each other while the seal member CL3 is sandwiched between the seal surfaces 33 s, 34 s and 35 s and a seal surface of the head cover 40. This suppresses a gap from being generated between the cam housing 30 and the head cover 40. The seal surfaces 33 s, 34 s and 35 s are an example of a second seal surface that sandwiches the seal member CL3 in cooperation with the head cover 40. Further, as will be described later in detail, seal surfaces 37 s and 38 s substantially parallel to the YZ plane are formed on the right side wall 33 and the left side wall 34 near the chain cover 60, respectively. Furthermore, the inner side surface of the right side wall 33 and the inner side surface of the left side wall 34 respectively include recessed regions 330 and 340 described later in detail.

FIG. 2B is a top view of the cylinder head 20. The cylinder head 20 includes a rear side wall 25 in addition to the above-described right side wall 23 and left side wall 24. The rear side wall 25 extends continuously to the right side wall 23 and the left side wall 24 in the X direction, and is located at an end of the cylinder head 20 in the −Y direction. The cylinder head 20 is provided, in its part surrounded by the right side wall 23, the left side wall 24, and the rear side wall 25, with holding holes 210 holding respective spark plugs for the respective cylinder, guide holes 211 guiding the respective intake valves, and guide holes 212 guiding the respective exhaust valves. Seal surfaces 23 s, 24 s, and 25 s are formed on the upper sides of the right side wall 23, the left side wall 24, and the rear side wall 25, respectively. The seal surfaces 23 s, 24 s and 25 s are continuous to one another and are substantially parallel to the XY plane.

FIG. 2B illustrates a seal member CL2 on the seal surfaces 23 s, 24 s, and 25 s. The seal member CL2 is made of rubber having oil resistance and is a Formed In Place Gasket (FIPG). The FIPG in a liquid state is applied to the seal surfaces 23 s, 24 s, and 25 s of the cylinder head 20 before the cam housing 30 is fastened, and is then hardened by heating or absorbing moisture in air, which is changed into an elastic body. The FIPG is a liquid gasket in such a manner. Additionally, the seal member CL2 is not limited to this, and may be a gasket made of acrylic rubber or the like as described above. On the seal surfaces 23 s, 24 s, and 25 s, a plurality of bolt holes, designated with no numerical reference, into which the bolts for fastening the cam housing 30 to the cylinder head 20 are formed. The seal member CL2 is located outside the plurality of bolt holes. The cylinder head 20 and the cam housing 30 are fastened to each other while the seal member CL2 is sandwiched between the seal surfaces 23 s, 24 s, and 25 s and a seal surface of the cam housing 30 in the −Z direction. This suppresses a gap from being generated between the cylinder head 20 and the cam housing 30. The seal surfaces 23 s, 24 s, and 25 s are an example of a first seal surface that sandwiches the seal member CL2 in cooperation with the right side wall 33, the left side wall 34, and the rear side wall 35. As will be described later, seal surfaces 27 s and 28 s substantially parallel to the YZ plane are formed on the right side wall 23 and the left side wall 24 near the chain cover 60, respectively.

FIG. 3A is a front view of the cylinder head 20 and the cam housing 30. FIG. 3A illustrates a lower side wall 29 of the cylinder head 20 extending in the X direction between the right side wall 23 and the left side wall 24. The seal surface 29 s of the lower side wall 29 located in the +Y direction is continuous to the above-described seal surfaces 27 s and 28 s. The seal surfaces 27 s, 28 s, and 29 s are substantially parallel to the XZ plane. In a state where the cylinder head 20 and the cam housing 30 are fastened to each other, the seal surfaces 27 s and 28 s of the cylinder head 20 and the seal surfaces 37 s and 38 s of the cam housing 30 are continuous to one another, and these seal surfaces 27 s, 28 s, 29 s, 37 s, and 38 s are substantially parallel in the XZ plane. FIG. 3A illustrates a seal member CL5 on the seal surfaces 27 s, 28 s, 29 s, 37 s, and 38 s. The seal member CL5 is, but not limited to, the same as the above-described seal member CL2.

FIG. 3B is a rear view of the chain cover 60. FIG. 3B illustrates a part of the chain cover 60 when viewed in the +Y direction. The chain cover 60 includes a seal surface 68 s that sandwiches the seal member CL5 in cooperation with the seal surfaces 27 s, 28 s, 29 s, 37 s, and 38 s. On the seal surfaces 27 s, 28 s, 29 s, 37 s, and 38 s and the seal surface 68 s, a plurality of bolt holes, designated with no numerical reference, into which bolts for fastening the chain cover 60 to the cylinder head 20 and the cam housing 30 are inserted are formed. The seal member CL5 is located outside the plurality of bolt holes. The chain cover 60 is fastened to the cylinder head 20 and the cam housing 30 while the seal member CL5 is sandwiched between the seal surfaces 27 s, 28 s, 29 s, 37 s, and 38 s and the seal surface 68 s. This suppresses a gap from being generated between the chain cover 60, and the cylinder head 20 and the cam housing 30.

As described above, a gap between the cylinder head 20 and the cam housing 30, a gap between the cam housing 30 and the head cover 40, and a gap between the chain cover 60, and the cylinder head 20 and the cam housing 30 are sealed. Thus, for example, the lubricating oil supplied to the camshafts 53 and 54 is prevented from leaking outside.

Next, a description will be given of the right side wall 33 of the cam housing 30 illustrated in FIG. 2A. FIG. 4A is a cross-sectional view taken along line A-A of FIG. 2A, This cross section is perpendicular to the direction in which the camshafts 53 and 54 extend. The right side wall 33 includes the recessed region 330, a curved region 331, and a linear region 332. The curved region 331 is continuous from the recessed region 330 to the upper side in the gravity direction. The linear region 332 is continuous from the curved region 331 to the upper side in the gravity direction. The curved region 331 and the linear region 332 are an example of an upper region continuous from the recessed region 330 to the upper side in the gravity direction. Both the recessed region 330 and the curved region 331 are curved, and the curvature radiuses are substantially the same. The inner side surface of the right side wall 33 is curved so as to gradually approximate verticality from the recessed region 330 to the curved region 331. The linear region 332 is slightly inclined relative to the gravity direction in cross section, but extends substantially linearly.

The recessed region 330 is recessed downward in the gravity direction. FIG. 4B is an enlarged view of the recessed region 330. FIG. 4B illustrates a horizontal line segment parallel to the X direction. Herein, the lubricating oil supplied to the camshafts 53 and 54 is splashed by the rotation of the camshafts 53 and 54. At least a part of the splashed oil is attached to the linear region 332 and the curved region 331 of the inner side surface of the right side wall 33, then flows downward in the gravity direction, and is retained in the recessed region 330. This ensures a time period during which the oil is in contact with the right side wall 33 until the oil overflows from the recessed region 330. Newly splashed oil is always retained in the recessed region 330.

Herein, the camshafts 53 and 54 are supplied with the oil from a plurality of paths, and the oil increases its temperature due to the combustion in the engine 1 while the oil is flowing through such paths. Thus, such high temperature oil retained in the recessed region 330 transmits the heat from the oil to the right side wall 33 of the cam housing 30, thereby promoting the heat exchange between the oil and the cam housing 30. Further, the recessed region 330 is formed to extend in the X direction in which the camshafts 53 and 54 extend. This ensures a contact area between the oil and the inner side surface of the right side wall 33 of the cam housing 30, which promotes the heat exchange between the oil and the cam housing 30. In addition, FIG. 4A illustrates splashed oil.

The heat exchange between the high temperature oil and the cam housing 30 is promoted in such a manner, whereby the temperature of the cam housing 30 increases. This suppresses an increase in a temperature difference between the cylinder head 20 and the cam housing 30, which suppresses an increase in a thermal expansion difference between the cylinder head 20 and the cam housing 30 due to this temperature difference. Herein, if the thermal expansion difference between the cylinder head 20 and the cam housing 30 increases, the seal surfaces 23 s, 24 s, and 25 s of the cylinder head 20 might be positionally displaced relative to the seal surface of the cam housing 30 opposite thereto. As a result, the seal member CL2 interposed between the seal surfaces might be damaged, and then the oil might leak between the cylinder head 20 and the cam housing 30. In the present embodiment, the increase in the thermal expansion difference is suppressed as described above, thereby suppressing such oil leakage.

Further, as illustrated in FIG. 4A, the recessed region 330 is formed at a position closer to the seal surface 23 s than the seal surface 33 s. It is thus possible to increase the temperature of the cam housing 30 around the seal surface 23 s of the cylinder head 20 and the seal surface of the cam housing 30 that face each other and might be a gap from which the oil leaks. This suitably suppresses the oil leakage.

Incidentally, unlike the seal surface of the cam housing 30 facing the seal surface 23 s of the cylinder head 20, the periphery of the seal surface 33 s of the cam housing 30 and the seal surface of the head cover 40 facing each other is distant away from the cylinder head 20. Therefore, in this periphery, the temperature difference and the thermal expansion difference between the cam housing 30 and the head cover 40 hardly increase and the oil leakage hardly occurs. Therefore, in the present embodiment, the recessed region 330 is formed in the periphery of the seal surface 23 s of the cylinder head 20, in which the oil leakage tends to occur.

FIG. 4A illustrates a line segment CL connecting between an inner edge of the seal surface 23 s and an inner edge of the seal surface 33 s. The curved region 331 and the linear region 332 are located outside the cam housing 30 with respect to the line segment CL. In other words, the curved region 331 and the linear region 332 protrude outside the cam housing 30 from the line segment CL. Therefore, the length of the inner side surface of the right side wall 33 is ensured, as compared with a case where a side wall has a linear shape along the line segment CL in cross sectional view. Herein, as described above, when the oil splashes the curved region 331 and the linear region 332, and then flows toward the recessed region 330. Since the length of the inner surface of the right side wall 33 is ensured, the time during which the oil is in contact with the curved region 331 and the linear region 332 is ensured. Therefore, even with this configuration, the heat exchange between the oil and the right side wall 33 of the cam housing 30 is promoted. In addition, like the recessed region 330, the curved region 331 and the linear region 332 also extend along the camshaft 53.

As illustrated in FIG. 4A, the linear region 332 is smoothly continuous to the recessed region 330 through the curved region 331. Accordingly, the oil attached on the linear region 332 and the curved region 331 promptly flows to the recessed region 330. Therefore, the oil is retained in the recessed region 330 before a large amount of the heat of the oil is absorbed to the linear region 332 and the curved region 331 of the right side wall 33, so a large amount of the heat of the oil is transmitted to the recessed region 330. This makes it possible to increase the temperature of the cam housing 30 around the seal surface 23 s of the cylinder head 20 and the seal surface of the cam housing 30 facing each other. This suitably suppresses the oil leakage.

Further, as illustrated in FIG. 4A, the inclination angle of the linear region 332 positioned above the recessed region 330 in the gravity direction is steeper than the inclination angle at an arbitrary point on the recessed region 330. In other words, the inclination angle of the linear region 332 is approximately 90 degrees with respect to the horizontal direction. Therefore, the oil attached on the linear region 332 promptly flows to the recessed region 330. This also suitably suppresses the oil leakage.

FIG. 5 is a cross-sectional view taken along line B-B of FIG. 2A. The left side wall 34 is substantially symmetrical with the right side wall 33 with respect to the YZ plane. Accordingly, like the right side wall 33, the inner side surface of the left side wall 34 also includes a recessed region 340, a curved region 341, and a linear region 342. This promotes the heat exchange between the oil and the left side wall 34 of the cam housing 30, which also suppresses the oil leakage between the seal surface 24 s of the cylinder head 20 and the seal surface of the left side wall 34 of the cam housing 30.

The increase in the thermal expansion difference between the cylinder head 20 and the cam housing 30 due to the temperature difference therebetween is suppressed as described above, which also suppresses the oil leakage between the seal surfaces 37 s and 38 s of the cam housing 30 and the seal surface 68 s of the chain cover 60. In addition, the heat exchange between the oil and the cam housing 30 suppresses an excessive increase in the temperature of the oil. This suppresses deterioration of the oil, and deterioration of the lubricity thereof due to an excessive decrease in the viscosity thereof.

Further, each surface area of the inner side surfaces of the right side wall 33 and the left side wall 34 is ensured, which also ensures an area of a surface with which blowby gas generated in the engine 1 contacts. Therefore, the blowby gas contacts with the inner side surfaces of the right side wall 33 and the left side wall 34, which promotes separation of oil from the blowby gas. This suppresses an increase in the oil consumption, and generation of White smoke due to introduction of the blowby gas into the intake system.

In the present embodiment, the rear side wall 35 is different from the right side wall 33 and the left side wall 34, but the rear side wall 35 may be configured similarly. With this configuration, it is possible to exchange the heat between substantially the entire cam housing 30 and the oil, which further suppresses the increase in the temperature difference between the cam housing 30 and the cylinder head 20.

In the present embodiment, the recessed region 330 is formed over substantially the entire region of the right side wall 33 extending in the Y direction, but is not limited thereto. For example, the recessed region 330 described above may be formed only in a part of the region of the right side wall 33 extending in the Y direction. For example, such a recessed region 330 may be formed at a position closer to the chain cover 60 than the rear side wall 35. This increases the temperature of the right side wall 33 of the cam housing 30 in the vicinity of the chain cover 60, which suitably suppresses the oil leakage between the cam housing 30 and the chain cover 60. The same applies to the recessed region 340 of the left side wall 34.

Next, a description rill be given of a cam housing 30 a according to a variation. FIG. 6A is a partial top view of the cam housing 30 a according to the variation. FIG. 6B is a cross-sectional view taken along line C-C of FIG. 6A. The cam housing 30 a is formed with ribs 347 on an inner surface of a left side wall 34 a. The ribs 347 extend downward in the gravity direction along the inner side surface of the left side wall 34 a, and protrude inside the cam housing 30 a. The ribs 347 are provided between the adjacent support walls 37. The provision of the ribs 347 in such a manner increases the area of the inner side surface of the left side wall 34 a. That is, the amount of the oil attachable to the inner side surface of the left side wall 34 a is ensured. This promotes the heat transmission from the oil to the left side wall 34 a, which suppresses the oil leakage.

In addition, the provision of the ribs 347 in the left side wall 34 a increases volume of the left side wall 34 a, which ensures rigidity thereof. The ensuring of the rigidity of the left side wall 34 a on the exhaust side suppresses vibration of the left side wall 34 a due to the combustion in the engine. This suppresses vibration noise of the head cover 40 due to the vibration transmission from the left side wall 34 a to the head cover 40.

The position of the rib 347 is not limited to the position illustrated in FIG. 6A, hut may be provided at a position distant from a bolt by which the cylinder head 20 and the cam housing 30 a are fastened. The reason for this is as follows: In the vicinity of the bolt, the increase in the thermal expansion difference between the cylinder head 20 and the cam housing 30 a is regulated to some extent by the fastening force of the bolt, whereas such fastening force might not be sufficient at a position distant from the bolt. Thus, the provision of the rib 347 at a position distant from the bolt ensures the surface area of the left side wall 34 a of the cam housing 30 a at a position distant from the bolt, which suppresses the increase in the thermal expansion difference between the cylinder head 20 and the cam housing 30 a at a position distant from the bolt.

Ribs similar to the ribs 347 may also be provided in the right side wall 33 on the intake side. This further suppresses the oil leakage. Also, the vibration of the right side wall 33 can be suppressed. However, the provision of such ribs might lead to an increase in the weight of the housing and to deterioration of the fuel consumption. Therefore, it is desirable to set the position, the size and, the number of ribs in consideration of the increase in the weight of the housing, the effect of suppressing the oil leakage, the effect of reducing the vibration, and the like. For example, the vibration caused by the combustion of the engine tends to be transmitted to the left side wall 34 a on the exhaust side, as compared with the right side wall on the intake side. Therefore, in this variation, in consideration of reducing the vibration of the left side wall 34 a on the exhaust side while suppressing the increase in the weight of the cam housing 30 a, the ribs 347 are provided only in the left side wall 34 a.

Although some embodiments of the present disclosure have been described in detail, the present disclosure is not limited to the specific embodiments but may be varied or changed within the scope of the present disclosure as claimed.

In the above embodiment and variation, the recessed region 330 is smoothly continuous to the curved region 331, but is not limited to such a shape. For example, the recessed region may be formed into a groove shape on a region of the inner surface of the sidewall that is substantially horizontal when viewed in cross section perpendicular to the direction in which the camshafts extend. Further, the inner side surface of the side wall may be curved such that the inclination angle gradually approximate horizontal from the upper side to the lower side in the gravity direction, and the recessed region may be defined by a shape that protrudes upward in the gravity direction from an inner edge of this curved region of the housing so as to stop the flow of oil to the inside of the housing. In the above embodiment and variation, the linear region 332 is formed into a substantially straight, but is not limited thereto, and may be formed into a curved shape. 

What is claimed is:
 1. An engine comprising: a cylinder head; a cam housing fastened to the cylinder head; a camshaft rotatably supported by the cam housing and supplied with lubricating oil; and a head cover fastened to the cam housing, wherein the cam housing includes a side wall extending along the camshaft, and an inner side surface of the side wall includes a recessed region recessed downward in a gravity direction.
 2. The engine of claim 1, wherein the cylinder head includes a first seal surface that sandwiches a first seal member in cooperation with the side wall, the side wall includes a second seal surface that sandwiches a second seal member in cooperation with the head cover, and the recessed region is provided at a position closer to the first seal surface than the second seal surface.
 3. The engine of claim 2, wherein the inner side surface of the side wall includes an upper region continuous from the recessed region to an upper side in the gravity direction, and the upper region is located outside the cam housing with respect to a line connecting an inner edge of the first seal surface and an inner edge of the second seal surface when viewed in a cross section perpendicular to a direction in which the camshaft extends.
 4. The engine of claim 3, wherein the inner side surface of the side wall is smoothly continuous from the upper region to the recessed region when viewed in the cross section perpendicular to the direction in which the camshaft extends.
 5. The engine of claim 1, wherein the recessed region extends along the camshaft.
 6. The engine of claim 1, wherein the side wall includes a rib partially projecting inside the cam housing.
 7. The engine of claim 6, wherein the side wall includes: an intake side wall located on an intake side; and an exhaust side wall located on an exhaust side, and the rib is provided on the exhaust side wall. 